Note: Descriptions are shown in the official language in which they were submitted.
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A PROCESS FOR SEPARATING BIOMASS COMPONENTS,
Field of Invention
The present invention relates to a process of separation of biomass into
individual
components such as cellulose, hemi-cellulose and lignin.
Background of Invention
Lignocellulosic biomass must be pre-treated to realize high yields vital to
commercial
success in biological conversion. Better pre-treatment can reduce use of
expensive
enzymes thus makes the process economically viable. Thus, more attention must
be
given to gaining insight into interactions among these operations and applying
that
insight to advance biomass conversion technologies that reduce costs. Although
many
biological, chemical, and physical methods have been tried over the years, pre-
treatment advances are still needed for overall costs to become competitive
with
conventional commodity fuels and chemicals.
Paper industries have standardized an alkaline pulping process for preparation
of
cellulose. There are pulping equipinents that can run in continuous operations
as well.
The pulping liquor used contains a very high percentage of alkali (NaOH) along
with
other chemicals. There are several problems with this approach because the
process is
not eco-friendly and the recovery of the alkali after treatment is very
expensive. The
pulping liquor damages the hemicellulose and results in the formation of sugar
degradation products. The recovery of lignin from the black liquor requires
acidification, which adds to the cost. The lignin recovered is also degraded
and is
therefore not in its native form. The process also results in some cellulose
loss.
Therefore, this pulping process cannot be used for the bio-refinery platform.
Of late, there is a renewed interest in ammonia pretreatment besides other
known
pretreatment process.
US patent application US 2008/0008783AI, by Bruce Dale et al. provides a
pretreatment process using concentrated ammonium hydroxide under pressure to
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improve the accessibility/ digestibility of the polysaccharides from a
cellulosic
biomass. It also uses a combination of anhydrous ammonia and concentrated
ammonium hydroxide solutions.
r
US patent application US 2007/0031918A1, by Dunson et al. provides a process
in
which the biomass at relatively high concentration treated with relatively low
concentration of ammonia relative to the dry weight of the biorimass. The
ammonia
treated biomass then digested with a saccharification enzyme to produce
fermentable
sugars. The process utilizes vacuum for better ammonia penetration and
recovery, it
also uses a plasticizer for softening.
US patent 5,473,061 to Bredereck et al. (1995) describes a process which
involves
bringing the cellulose in contact with liquid ammonia at a pressure higher
than
. atmospheric pressure in a pressure vessel and subsequent expansion by rapid
reduction
of the pressure to atmospheric pressure to activate the cellulose for
subsequent
chemical reactions.
Dale in US patent nos. 4,600,590 and 5,037,663 describes the use of various
volatile
chemical agents to treat the cellulose containing materials, particularly
ammonia by
what came to known as the AFEX process (ammonia freeze or ammonia fiber
explosion).
US patent 5,171,592 to Holtzapple et al. (1992) provides an AFEX process in
which the
biomass is treated with liquid ammonia or any other appropriate swelling
agent,
exploded and the swelling agent and the treated biomass are recovered.
US patent 5,366,588 uses two stages to hydrolyze the hemicellulose sugars and
the
cellulosic sugars in a countercurrent process were using a batch reactor, and
results in
poor yield of glucose and xylose using a mineral acid. Further, the process
scheme is
complicated and the economic potential in large scale to produce inexpensive
sugars for
fermentation is low.
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US patent 5,188,673 employs concentrated acid hydrolysis, which has benefits
of high
conversion of biomass, but suffers from low product-yields due to degradation
and the
requirement of acid recovery and recycle. Sulphuric acid concentrations used
are 30 -
70 weight percent at temperatures less than 100 C.
Elian et al. US patent 2,734,836 discloses a process where acid used to
pretreat
lignocellulosic material to extract pentoses using acetic acid. The material
is sprinkled
with the acid and heated to 80 - 120 C and the acid is recycles through the
cooker in a
manner to preserve the cellulose fibers. The residual material is used in
conventional
pulping.
Eickemeyer US patent 3,787,241 discloses a percolator vessel for decomposing
portions of wood. The first stage is the hydrolysis of hemicellulose to xylose
using 1%
sulphuric acid and then acid hydrolysis of cellulose occurs and lignin remains
in the
reactor throughout the hydrolysis and removed at the end.
Wright US patent 4,615,742 discloses a series of hydrolysis reactors. Some of
these
are prehydrolysis reactors and are for removing hemicellulose while others are
for
hydrolysis. Because the contents move in a series, the duration of each step
is the
same. The process does not remove lignin from the solids and multiple reactors
are
required.
Objects of the present invention
The main object of the present invention is to provide a process for process
for
separating biomass components such as cellulose, hemicellulose and lignin.
Another object of the present invention.is to reduce the treatment time and
eliminate
ttie formation of sugar degradation products like furfurals.
One more object of the present invention is to provide a process to hydrolyze
hemicellulose in the lignocellulosic material to pentose sugars.
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Summary of Invention
The present invention provides a process for separating lignocellulosic
biomass derived
from various sources like sweet sorghum bagasse, rice straw, wheat straw,
sugar cane
bagasse, corn stover, miscanthus, switch grass and various agricultural
residues into its
major components namely cellulose, hemicellulose and lignin in a specially
designed
pretreatment set up. The said process comprises of the following steps, (i)
contacting
the biomass such as herein described with an alkaline agent capable of
dissolving
essentially lignin in said biomass under predetermined temperature and
pressure to
dissolve and remove lignin; (ii) reacting with mild acid under predetermined
temperature and pressure with the remaining residue of step (i) to hydrolyze
hemicellulose and subsequently removing from the biomass; (iii) the residual
solid
should contain reactive cellulose with minimum impurities of hemicellulose and
lignin
in its native form.
Brief description of drawings
Figure I is an exemplary illustration of the system of separating biomass
components
according to an embodiment of the present invention.
Detailed Description of the Invention
Accordingly, the present invention provides a process for separating biomass
components namely cellulose, hemicellulose and lignin, said process comprising
steps
a) contacting biomass with an alkaline agent capable of dissolving essentially
lignin in said biomass under predetermined temperature and pressure to
dissolve
and remove lignin under pressure in ammonia solution;
b) reacting with mild acid under predetermined temperature and pressure with
the
remaining residue of step (a) to hydrolyze hemicellulose and subsequently
removing the same from biomass
c) obtaining highly reactive cellulose from the remaining biomass.
In an aspect of the present invention, the alkaline agent selected from the
group
comprising ammonia and ammonia derivatives such as amines.
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In another aspect of the present invention the alkaline agent is contacted
with the
biomass at a temperature in the range of 90 C to 200 C. -
In still another aspect of the present invention, the predetermined pressure
is in the
range of 7.5 - 25 Bar.
In yet another aspect of the present invention the alkaline agent contacted
with the
biomass for a period of 1 to 30 minutes and preferably, the alkaline agent
contacted
with the biomass for a period of 5 to 10 minutes.
10In a further aspect of the present invention, concentration of aqueous
ammonia is in the
range of 10% to 30%.
In still another aspect of the present invention, the dissolved lignin is
separated under
pressure in ammonia solution.
In yet another aspect of the present invention the mild acid selected from a
group
comprising mineral acids having concentration in the range of 0.25%- 2%.
In another aspect of the present invention, the mild acid is reacted with the
residual
biomass at a temperature in the range of 120 - 200 C.
In still another aspect of the present invention the mild acid is reacted with
the residual
bio mass at a pressure in the range of 1.5 - 20 Bar.
In yet another aspect of the present invention the mild acid is reacted with
the residual
biomass for a period of up to 15 min.
In a further aspect of the present invention, the hemicellulose is obtained in
the form of
pentose sugars.
In a further more aspect of the present invention, the lignin is present in
its native form.
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In another advantageous aspect of the present invention, formation of sugar
degradation
product is substantially eliminated.
In still another aspect of the present invention, the residue obtained is
amenable for
enzymatic saccharification.
The present invention also provides a system for separating biomass
comprising:
(a) a reactor chamber for containing biomass having at least one inlet and at
least
one outlet;
(b) at least one cylinder for storing alkaline agent; said cylinder is in
fluid flow
communication with the inlet of the reactor chamber for supplying alkaline
agent to the reactor chamber for dissolving lignin;
(c) a reservoir suitable for containing water and/or mild acid; said reservoir
is in
fluid flow communication with the inlet of the reactor chamber for supplying
water and/or acid to reactor chamber to hydrolyze hemicellulose;
(d) A receiver coupled to the outlet of the reactor chamber for receiving
dissolved
lignin or hydrolyzed hemicellulose from the reactor chamber;
wherein the flow connections between the inlet of the reactor chamber and bank
cylinder, reservoir and boiler adapted to operate in tandem.
In another embodiment of the present invention, a boiler is in fluid flow
communication with the inlet of the reactor chamber for supplying steam to the
reactor
chamber.
In still another embodiment of the present invention, the receiver is in fluid
flow
communication with the boiler.
In yet another embodiment of the present invention comprising an ammonia
absorption
system comprising of a surge tank, hydrocyclone and two absorbers to recover
and
recycle ammonia.
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According to a preferred embodiment, the present invention relates to a
process in
which the lignocellulosic biomass subjected to a two-stage treatment process
(i) ammonia treatment in which most of the lignin present in the biomass is
dissolved and removed by a under pressure filtration process;
(ii) acid treatment of the residue obtained from the first step to hydrolyze
most
of the hemicellulose in the biomass as pentose sugars without the formation
of sugar degradation products and obtain a residue containing mostly
cellulose, which is highly reactive
The process of the present invention utilizes lignocellulosic biomass such as
sweet
sorghum bagasse, rice straw, wheat straw, sugar cane bagasse, corn stover,
miscanthus,
switch grass and various agricultural residues. Preferably, the materials
comminuted
irrto particles before treatment.
Following table discloses a typical biomass composition.
Typical biomass composition
Biomass type Cellulose% Hemicellulose% Lignin%
Sweet sorghum
41.10% 25.91% 20.27%
bagasse
Rice straw 36.25% 17.67% 28.80%.
Maize stalks 35.65% 19.87% 22.25%
In the process of the present invention, the biomass treated with alkaline
agent under
predetermined temperature and pressure to dissolve lignin under pressure. The
alkaline
agent can be any suitable alkaline agent capable of dissolving lignin.
Alkaline agent
such as ammonia or ammonia derivatives such as amines. Alkaline agent treated
with
biomass at a temperature in the range of 90 to 200 C and at a pressure in the
range of
7.5 to 25 Bar. The treatment time of biomass by alkaline agent is in the range
of 1 to 30
minutes. Preferably, the treatment time of biomass by alkaline agent is in the
range of 5
to 10 minutes. In a preferred embodiment of the present invention, aqueous
ammonia
can be used as an alkaline agent in a concentration in the range of 10 to 30%.
Under
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high temperature and pressure, lignin of the biomass dissolves in alkaline
agent.
Thereafter, the alkaline agent filtered under high pressure by high-pressure
filtration
process.
The residual biomass obtained after alkaline agent treatment or ammonia
treatment is
reacted with mild acid or water at a predetermined temperature and pressure.
Mild acid
or water hydrolyzes the hemicellulose. Water or any type of mineral acid can
be used
for hydrolyzing hemicellulose. Preferably the mineral acids having
concentration in the
range of 0.25% - 2% can be used. The residual biomass can be treated with mild
acid at
a temperature in the range of 120 - 200 C and at a pressure in the range of
1.5 - 20
Bar. The biomass can be treated with'acid for a period in the range of 1 to 30
minutes
and preferably in the range of 10 to 15 minutes. Majority of the hemicellulose
hydrolyzed into pentose sugars.,
one of the advantageous aspect of the invention, the cellulose thus obtained
is highly
reactive for enzymatic saccharification.
In conventional ammonia treatment. process as described in the prior art, the
lignocellulosic biomass treated with high/ low concentrations of aqueous or
anhydrous.
ammonia under high pressure and then pressure is released rapidly (explosion)
to obtain
a residue that is highly reactive. The lignin in these processes is re-
precipitated in the
biomass and is not separated. Whereas, in a preferred embodiment of the
present
irrvention, lignocellulosic biomass treated with aqueous ammonia under high
pressure
and the lignin dissolved in the process separated by a unique under pressure
filtration
process along with the ammonia solution; thereby re-precipitation of lignin is
avoided.
According to an embodiment of the present invention, the lignocellulosic
material
treated with aqueous ammonia with a concentration of at least 10% and
preferably
30%.* The reaction temperature for the ammonia treatment can be between 90 -
200 C
30, and preferably, 120 C.The pressure during the ammonia treatment is between
7.5 Bar
to 22 Bar however pressure of 15 Bar is preferable.
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The lignocellulosic biomass taken in the reactor and ammonia solution added to
give a
solid concentration of preferable 15% and heated to the reqUired condition by
direct
steam injection from the boiler. After holding for preferably 10 min in the
desired
condition the ammonia solution filtered under pressure, which contains
dissolved
lignin, the remaining residue consists of mostly cellulose and hemicellulose.
When the
ammonia in the solution recovered using the ammonia absorption system the
lignin
precipitates.
The lignin obtained during the ammonia treatment by under pressure filtration
process
has very little modifications. In other words the lignin thus obtained exists
in its native
form.
7'he conventional process for the hydrolysis of hemicellulose utilized either
concentrated acid treatment or mild acid treatment at high temperatures. These
processes result in the formation of sugar degradation products. In the
present process,
the residue obtained after step one, subjected mild acid treatment at high
temperatures
for short time to hydrolyze most of the hemicellulose in the residue to
pentose sugar
with mininial formation of degradation products.
The process of the present invention utilizes aqueous solution of acid
(sulphuric acid,
hydrochloric acid or nitric acid or any other strong acid, which can give a pH
of 2) for
the hydrolysis of hemicellulose. Sulphuric acid is preferred, and when
sulphuric acid
used as the acid catalyst the concentration of acid is between 0.25% - 2%,
usually 1%
acid concentration is preferred.
The re'sidue obtained after step 1(ammonia treatment) is added with preferable
1%
sulphuric acid and heated to a temperature of 120 - 200 C, preferably 145 C
by live
steam injection. The contents maintained at the said condition for 10 - 30
minutes;
however the preferred time is 15 min. After the holding time the contents
filtered under
pressure to get a residue rich in highly reactive cellulose and a filtrate
that contains
mostly hemicellulose as pentose sugars. The unique under pressure filtration
process
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helps in rapid cooling and thereby reducing the formation of sugar degradation
products.
The pretreated material obtained after the unique two-stage pretreatment
process of the
present invention is rich in reactive cellulose, which is evident from its
susceptibility to
enzymatic saccharification.
The following paragraphs describe a reactor system of the present invention
with
reference to figure 1.
As can be observe from figure 1, the system of separating biomass components
of the
present invention comprises a reactor chamber. Said reactor chamber can be a
versatile
digester (D4) which is suitable for acid hydrolysis, steam explosion, solvent
treatment
etc. Biomass, which is to be treated, kept in the reactor chamber or versatile
digester.
The reactor chamber has at least one inlet and at least one outlet. The inlet
of the
reactor chamber is in fluid flow communication with a cylinder in which
alkaline agent
is being stored. More than one cylinder can be used for storing the alkaline
agent. The
facility of storing the alkaline agent depicted in figure 1 as a central
facility for storing
aminonia gas (C101). This facility used for supplying alkaline agent in the
reactor
chamber.
Further, the reactor chamber provided with an inlet for supplying water and/or
mild
acid into the reactor chamber. A separate reservoir or. storage facility (not
shown in the
figure) can be provided for storing water and/or mild acid. Said reservoir is
in fluid
flow communication with an inlet of the reactor chamber for supplying water
and/or
rriild acid in the reactor chamber to hydrolyze hemicellulose. A boiler (102)
coupled to
an inlet of the reactor chamber for supplying steam at a predetermined
temperature and
pressure. For collecting the dissolved lignin and/or hydrolyzed hemicellulose
from the
reactor chamber a receiver provided. Said receiver coupled to the outlet of
the reactor
chamber.
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11' ammonia is used as an alkaline agent in the present process, then an
ammonia
absorption system can be provide to recover and recycle ammonia. The ammonia
absorption system comprises a surge tank, hydro-cyclone and two absorbers.
Examples
Example 1 - Effect of different ammonia concentrations on sweet sorghum
bagasse with increased treatment time
About 100 g sweet sorghum bagasse was loaded in the pre-treatment reactor. The
particle size of the bagasse used was in the range of 0.5 - 1 mm. To this
biomass
different concentration of ammonia either 10% or 20% or 30% were added. The
amount o1' different ammonia solutions added was such as to give a final solid
concentration of 15%. The reactor then heated to attain of pressure of 7.5 Bar
in all the
cases. The temperatures attained for 10, 20 and 30% ammonia were 140, 120 and
90 C
respectively. Direct steam injection employed to heat the reactor. The
contents in the
reactor held at the said conditions for an extended time of 30 min. After the
holding
time the contents filtered under pressure and the hydrolysate collected in a
receiver.
The hydrolysates/ filtrates analyzed for cellulose and hemicellulose present
by sugar
analysis. The residue obtained analyzed for cellulose, hemicellulose and
lignin. The
results is given in table 3.
Table I gives the percentage (%) removal of cellulose, hemicellulose and
lignin in the
different pretreated residues when compared to the starting material.
Table 1
Ammonia Pressure Temperature % removal of biomass components
concentration (bar) C Cellulose Hemicellulose Lignin
7.5 140 17.73% 15.54% 42.48%
10% 11 160 20.45% 19.67% 55.84%
15 180 25.41% 22.96% 58.59%
20% 7.5 120 24.71% 16.71% 43.53%
10 126 20.28% 14.29% 45.66%
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Ammonia Pressure Temperature % removal of biomass components
concentration (bar) C Cellulose Hemicellulose Lignin
15 145 19.78% 28.50% 61.67%
20 160 29.84% 44.29% 69.80%
7.5 90 19.17 10.77 37.59
30% 15 120 18.85 39.91 60.90
22 140 22.44 47.99 76.07
Example 2 - Sulphuric acid treatment at higher temperatures
The biomass (100g), sweet sorghum bagasse of 0.5 - 1 mm particle size, was
loaded in
the pre-treatment reactor to this 1% (v/v) sulphuric acid was added to get a
final
concentration of 15%. The contents in the reactor heated to 140 C or 160 C
using direct
steam injection. The contents held at the said temperatures for 10 min. After
that, the
contents filtered under pressure to get the acid hydrolysate and residue. The
hydrolysates/ filtrates analyzed for cellulose and hemicellulose present by
sugar
analysis. The residue obtained analyzed for cellulose, hemicellulose and
lignin. The
results are given in table 2.
Table 2 gives the % removal of cellulose, hemicellulose and lignin in the
pretreated
residues when compared to the starting material.
Table 2
% removal of biomass components
Temperature
Cellulose Hemicellulose Lignin
140 C 35.56% 59.30% 21.40%
160 C 32.24% 81.19% 29.20%
Example 3 - Two-stage process for the separation of biomass components
[n the pre-treatment reactor 100g of sweet sorghum bagasse of size 0.5 - 1
rrim was
loaded. To this 30% ammonia solution added to give a final solid concentration
of 15%.
The contents of the reactor then heated to achieve a temperature of 120 C (the
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corresponding pressure at that temperature was 15 Bar) by direct steam
injection. The
contents held at that. temperature for 10 min and then filtered under
pressure. The
hydrolysate collected in the receiver.
After the under pressure filtration process the residue was washed. with steam
to
remove the residual ammonia and then the reactor was cooled by passing cold
water in
the jacket. After cooling the reactor, 1% sulphuric acid pumped in to achieve
a solid
concentration of 15%. The contents heated to 140 C or 160 C by direct steam
injection. The contents held at the said temperature for 10 min and then
filtered under
= pressure.I'he acid hydrolysate collected separately.
The hydrolysates/ filtrates analyzed for cellulose and hemicellulose present
by sugar
analysis. The residue obtained analyzed for cellulose, hemicellulose and
lignin. The
results are given in table 3.
Table 3 gives the percentage (%) removal of cellulose, hemicellulose and
lignin in the
pretreated residues when compared to the starting material.
Table 3
% removal of
Condition Biomass component biomass
components
Ammonia - Cellulose 24.96%
Acid Hemicellulose 68.05%
(140 C) Lignin 64.89%
Ammonia - Cellulose 22.22%
Acid Hemicellulose 81.02%
(160 C) Lignin 67.88%
.
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Example 4 - Two-stage process for the separation of biomass components at
higher scale
In the pre-treatment reactor 1000g of sweet sorghum bagasse of size 0.5 - I mm
was
loaded. To this 30% ammonia solution added to give a final solid concentration
of 15%.
The contents of the reactor then heated to achieve a temperature of 120 C (the
corresponding pressure at that temperature was 15 Bar) by direct steam
injection. The
contents held at that temperature for 10 min and then filtered under pressure.
The
hydrolysate collected in the receiver.
After the under pressure filtration process the residue was washed with steam
to
remove the residual ammonia and then the reactor was cooled by passing cold
water in
the jacket. After cooling the reactor, 1% sulphuric acid pumped in to achieve
a solid
concentration of 15%. The contents then heated to 140 C by direct steam
injection.
The contents held at the said temperature for 15 min and then filtered under
pressure.
I'fie acid hydrolysate collected separately.
The hydrolysate/ filtrates analyzed for cellulose and hemicellulose present by
sugar
analysis. The residue obtained analyzed for cellulose, hemicellulose and
lignin. The
result is given in table 4.
Table 4 gives the percentage (%) removal of cellulose, hemicellulose and
lignin in the
pretreated residues when compared to the starting material.
Table 4
I % removal of biomass
Biomass component
components
Cellulose 12.12%
Hemicellulose 79.73%
Lignin 79.32%
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Example 5 - Susceptibility of pretreated residue to enzymatic saccharification
The final pretreated residue obtained after the two stage pretreatment process
in
example 6 digested with the enzyme commercial cellulose enzyme preparation to
check
the susceptibility of the residue for enzymatic saccharification. A 10% slurry
was
prepared and to this 60 FPU/g of the enzyme was loaded. The contents incubated
at
50 C at a pH of 4.5 for a period of 24 hrs. After the incubation time the
sugars were to
estimate the saccharification percentage. There was 85.3% saccharification in
24hrs,
which clearly indicates the susceptibility of the pretreated residue to the
cellulose
enzyme.
Advantages of the present invention:
1. The process of the present invention ammonia treatment will not use
explosive
steps so the ammonia recovery will be very easy.
2. The process of the present invention separates all the ingredients like
cellulose,
hemi-cellulose and lignin at a time and converts hemi-cellulose to peritose
sugar.
3. The process of the present invention does not require supercritical
ammonia.
4. Process of the present invention separates all three ingredients such as
lignin,
cellulose and pentose sugars with high purity.
5. There is no loss in quality of ingredients in the process of the present
invention.
6. In the process of the present invention, formation of sugar degrading
products is
minimal.
7. The alkaline agent solution used in the process of the present invention
can be
recovered very easily.
8. The alkaline agent solution used in the process of the present invention is
responsible for the-separation of the lignin resulting in high purity
cellulose.
9. Lignin recovered by the process of the present invention is of very high
purity
and there is no re-deposition because the dissolved lignin removed -under
pressure.
10. In the present invention, lignin removed without affecting the other
biomass
components.
11. Cellulose obtained in the present invention is very reactive.
